Windows - Security - Mitigate MpSigStub Vulnerability (CVE-2023-38175)

What the MpSigStub vulnerability remediation does

This Automox Worklet™ removes the vulnerable MpSigStub.exe file from Windows endpoints where Microsoft Defender is disabled. The Worklet targets CVE-2023-38175, an elevation of privilege vulnerability affecting the Microsoft Defender signature stub component located at %SystemRoot%\Sysnative\MpSigStub.exe.

The Worklet specifically addresses environments where organizations have disabled Microsoft Defender in favor of third-party antivirus solutions. When Defender is disabled, MpSigStub.exe cannot receive automatic security updates through Defender's built-in malware definition updates, leaving the vulnerable file on the endpoint. The Worklet checks Defender's status using the Get-MpComputerStatus cmdlet and removes the file only when Defender is confirmed to be disabled.

This approach follows Microsoft's official guidance for remediating CVE-2023-38175 in environments where Defender is not the primary security solution.

Why remove MpSigStub.exe on unmanaged endpoints

CVE-2023-38175 represents an elevation of privilege vulnerability that attackers can exploit to gain higher-level permissions on compromised endpoints. This vulnerability specifically affects the MpSigStub.exe component, which remains on the system even when Microsoft Defender is disabled.

Organizations using third-party antivirus solutions face a unique challenge. When you disable Microsoft Defender to avoid conflicts with your chosen security software, the MpSigStub.exe file loses its update mechanism. Microsoft's automatic signature updates only apply to endpoints with Defender enabled. This creates a security gap where a known vulnerable component persists without the ability to receive patches.

Removing the vulnerable file eliminates the attack surface entirely. This mitigation is particularly important for organizations subject to compliance frameworks that require remediation of known CVEs within specific timeframes. The Worklet provides automated detection and removal across your endpoint fleet, reducing manual effort and verification time compared to traditional vulnerability management processes.

How MpSigStub.exe removal works

1. Evaluation phase: The Worklet queries the AntivirusEnabled property using PowerShell's Get-MpComputerStatus cmdlet to determine Microsoft Defender's operational status. If Defender is disabled, the Worklet checks for the existence of MpSigStub.exe in the system directory using [System.IO.File]::Exists(). Endpoints with Defender enabled or with the file already removed report as compliant. Only endpoints with disabled Defender and the vulnerable file present trigger remediation.

2. Remediation phase: The Worklet executes [System.IO.File]::Delete() to remove the MpSigStub.exe file from $env:SystemRoot\Sysnative\MpSigStub.exe. After deletion, the Worklet verifies removal by checking for file existence again. If the file no longer exists, remediation is reported as successful. If deletion fails or the file persists, the Worklet logs the failure and returns an error state. The remediation includes error handling to catch permission issues or file locks that might prevent deletion.

CVE-2023-38175 remediation requirements

• Windows endpoints with Microsoft Defender disabled

• Third-party antivirus software installed and active

• Administrator privileges for file deletion

• PowerShell execution permissions for Get-MpComputerStatus cmdlet

• Windows Server or Workstation operating systems

• Critical: Only deploy this Worklet on endpoints where Microsoft Defender is disabled. Do not run on endpoints with active Defender protection.

Expected endpoint state after vulnerability mitigation

After successful remediation, the MpSigStub.exe file will no longer exist on the endpoint at %SystemRoot%\Sysnative\MpSigStub.exe. You can verify removal by checking the Worklet execution logs in the Automox console, which will display the message MpSigStub.exe file was successfully removed for successfully remediated endpoints.

The endpoint remains protected by your third-party antivirus solution. Normal system operations continue unaffected since the removed file is only used when Microsoft Defender is active. If you later re-enable Microsoft Defender, MpSigStub.exe will be automatically replaced only when signature updates are delivered through Microsoft Update or WSUS. The file will not be restored through standalone Mpam-fe.exe installations or UNC path-based updates.

Vulnerability scanners will no longer detect CVE-2023-38175 on remediated endpoints. This mitigation aligns with NIST guidance for addressing known vulnerabilities when patches cannot be applied through traditional update mechanisms.

How to validate mitigate mpsigstub vulnerability (cve-2023-38175) changes

1. Run this Worklet on a pilot Windows endpoint and review evaluation output for mitigate mpsigstub vulnerability (cve-2023-38175).

2. Confirm Automox activity logs show successful completion and exit code 0.

3. Verify endpoint state using checks aligned to evaluation script logic, such as Get-MpComputerStatus, Select-Object, Write-Output.

4. Validate remediation effects from script operations such as Get-MpComputerStatus, Select-Object, Write-Output, then rerun evaluation for compliance.